Inverted polymer photovoltaic cell and method for preparation thereof

ABSTRACT

An inverted polymer photovoltaic cell (or solar cell) includes an anode; a first anodic interlayer (buffer layer) based on PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; an active layer having at least one photoactive organic polymer as an electron donor and at least one electron acceptor organic compound; a cathodic interlayer (buffer layer); and a cathode. A second anodic interlayer (buffer layer) includes at least one heteropolyacid and, optionally, at least one amino compound is placed between the first anodic interlayer (buffer layer) and the active layer. 
     The inverted polymer photovoltaic cell (or solar cell) shows good values of photoelectric conversion efficiency (power conversion efficiency—PCE) (η) and, in particular, a good level of adhesion between the different layers, more specifically between the active layer and the first anodic interlayer (buffer layer).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. § 371 National Stage patentapplication of International patent application PCT/IB2021/057247, filedon 6 Aug. 2021, which claims priority to Italian patent application102020000020062, filed on 12 Aug. 2020, the contents of which are herebyincorporated in their entirety.

TECHNICAL FIELD

The present disclosure relates to an inverted polymer photovoltaic cell(or solar cell).

More particularly, the present disclosure relates to an inverted polymerphotovoltaic cell (or solar cell) comprising an anode; a first anodicinterlayer (buffer layer) based on PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; an activelayer comprising at least one photoactive organic polymer as an electrondonor and at least one organic electron acceptor compound; a cathodicinterlayer (buffer layer); a cathode; wherein a second anodic interlayer(buffer layer) comprising at least one heteropolyacid and, optionally,at least one amino compound is placed between said first anodicinterlayer (buffer layer) and said active layer.

Said inverted polymer photovoltaic cell (or solar cell) shows goodvalues of photoelectric conversion efficiency (power conversionefficiency—PCE) (η) and, in particular, a good level of adhesion betweenthe different layers, more specifically between the active layer andsaid first anodic interlayer (buffer layer).

The present disclosure also relates to a process for the preparation ofthe previously mentioned inverted polymer photovoltaic cell (or solarcell).

BACKGROUND

Photovoltaic devices (or solar devices) are devices capable ofconverting the energy of a light radiation into electrical energy.Currently, most photovoltaic devices (or solar devices) usable forpractical applications exploit the physico-chemical properties ofphotoactive inorganic materials, in particular high purity crystallinesilicon. However, due to the high production costs of silicon,scientific research has for some time been orienting its efforts towardsthe development of alternative organic materials with a polymericstructure [the so-called polymeric photovoltaic cells (or solar cells)].In fact, unlike high purity crystalline silicon, said organic materialsare characterized by a relative ease of synthesis, a low productioncost, a reduced weight of the related photovoltaic device (or solardevice), as well as allowing the recycling of said organic materials atthe end of the life cycle of the device in which they are used.

The above advantages therefore make the use of said organic materialsenergetically and economically attractive despite any lowerphotoelectric conversion efficiency (η) of the solar radiation oforganic photovoltaic devices (or solar devices) obtained with respect toinorganic photovoltaic devices (or solar devices).

The operation of organic photovoltaic devices (or solar devices) suchas, for example, polymeric photovoltaic cells (or solar cells), is basedon the combined use of an electron acceptor compound and an electrondonor compound.

In the state of the art, the electron donor compound most commonly usedin the construction of polymeric photovoltaic cells (or solar cells) isthe regioregular poly(3-hexylthiophene) (P3HT). This polymer hasexcellent electronic and optical characteristics [e.g., good values ofthe HOMO and LUMO orbitals, good molar absorption coefficient (ε)], goodsolubility in the solvents that are used to manufacture polymericphotovoltaic cells (or solar cells), and a fair mobility of the electronholes.

Other examples of polymers which can be advantageously used as electrondonor compounds are: the polymer PCDTBT{poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]},the polymer PCPDTBT{poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]},the polymer PffBT4T-2OD{poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)]},the polymer PBDB-T{poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]}.

In the state of the art, the electron acceptor compounds most commonlyused in the production of polymeric photovoltaic cells (or solar cells)are derivatives of fullerene such as, for example,[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM),[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). Said fullerenesderivatives have led to the greatest photoelectric conversionefficiencies (η) when mixed with electron donor compounds selected fromπ-conjugated polymers such as, for example, polythiophenes (η>5%),polycarbazoles (η>6%), derivatives ofpoly(thienotiophene)benzodithiophene (PTB) (η>8%), fluorinated polymersof benzothiadiazole (η>10%).

The elementary process of converting light into electric current in apolymeric photovoltaic cell (or solar cell) occurs through the followingstages:

-   -   1. absorption of a photon by the electron donor compound with        the formation of an exciton, i.e. a pair of electron-electron        hole charge carriers;    -   2. diffusion of the exciton in a region of the electron donor        compound up to the interface with the electron acceptor        compound, where its dissociation can take place;    -   3. dissociation of the exciton in the two charge carriers:        electron (−) in the accepting phase (i.e. in the electron        acceptor compound) and electron hole (+) in the donor phase        (i.e. in the electron donor compound);    -   4. carrying the charges thus formed to the cathode [electron (−)        through the electron acceptor compound] and to the anode        [electron hole (+) through the electron donor compound], with        generation of an electric current in the circuit of the        polymeric photovoltaic cell (or solar cell).

The photoabsorption process with the formation of the exciton andsubsequent transfer of the electron to the electron acceptor compoundinvolves the excitation of an electron from the HOMO (Highest OccupiedMolecular Orbital) to the LUMO (Lowest Unoccupied Molecular Orbital) ofthe electron donor compound and, subsequently, the transition from thisto the LUMO of the electron acceptor compound.

Since the efficiency of a polymeric photovoltaic cell (or solar cell)depends on the number of free electrons that are generated bydissociation of the excitons, one of the structural characteristics ofelectron donor compounds that most affects this efficiency is the energydifference between the HOMO and LUMO orbitals of the electron donorcompound (so-called band-gap). From this difference depends, inparticular, the wavelength of the photons that the electron donorcompound is able to collect and efficiently convert into electricalenergy (the so-called photon harvesting or light harvesting process).

From the point of view of electronic characteristics, the improvementsrelated to the materials used in the realization of polymericphotovoltaic cells (or solar cells) are possible through the design ofthe molecular structure of the electron donor compound and of theelectron acceptor compound in order to regulate optimal energy levels(HOMO-LUMO) of both. In particular, to obtain the dissociation of theexciton formed in the process and avoid the re-transfer of charge, it isnecessary that the difference both between the HOMO of the electrondonor compound and of the electron acceptor compound, and between theLUMO of the electron donor compound and of the electron acceptorcompound, must have an optimal value between 0.3 eV and 0.5 eV.Furthermore, the band-gap, i.e. the difference in energy between HOMOand LUMO of the electron donor compound, on the one hand must not be toohigh to allow the absorption of the greatest number of photons, on theother hand, it must not be too low because it could decrease the voltageat the polymeric photovoltaic cell (or solar cell) electrodes.

Another important characteristic of the materials used in theconstruction of polymeric photovoltaic cells (or solar cells) is themobility of electrons in the electron acceptor compound and of theelectron holes in the electron donor compound, which determines the easewith which the electric charges, once photogenerated, reach theelectrodes.

Electron mobility, i.e. the mobility of electrons in the electronacceptor compound and of the electron holes in the electron donorcompound, as well as being an intrinsic property of molecules, is alsostrongly influenced by the morphology of the active layer that containsthem, which in turn depends on the mutual miscibility of the compoundsused in said active layer and on their solubility. To this end, thephases of said active layer must neither be too dispersed nor toosegregated.

The morphology of the active layer is also critical as regards theeffectiveness of the dissociation of the photogenerated pairs electronhole-electron. In fact, the average lifetime of the exciton is such thatit is able to diffuse into the organic material for an average distancenot exceeding 10 nm-20 nm. Consequently, the phases of the electrondonor compound and the electron acceptor compound must be organized intonanodomains of comparable size with this diffusion distance.Furthermore, the contact area of the electron donor compound-electronacceptor compound must be as large as possible and there must bepreferential paths to the electrical contacts. Furthermore, thismorphology must be reproducible and must not change over time.

In the simplest way of operating, polymeric photovoltaic cells (or solarcells) are manufactured by introducing between two electrodes, usuallyconsisting of indium tin oxide (ITO) (anode) and aluminum (Al)(cathode), a thin layer (about 100 nanometers) of a mixture of theelectron acceptor compound and the electron donor compound (bulkheterojunction)]. Generally, in order to create a layer of this type, asolution of the two components (i.e. electron acceptor compound andelectron donor compound) is prepared and, subsequently, an active layeris created on the anode [indium-tin oxide (ITO)] starting from thissolution, using appropriate deposition techniques such as, for example,spin-coating, spray-coating, ink-jet printing, slot die coating, gravureprinting, screen printing, and the like. Finally, the counter-electrode[i.e. the aluminum cathode (Al)] is deposited on the dried active layerby means of known techniques, for example, by evaporation. Optionally,between the anode and the active layer and/or between the cathode andthe active layer, other additional layers can be introduced (calledinterlayers or buffer layers) capable of performing specific functionsof an electrical, optical, or mechanical nature.

Generally, for example, in order to favor the reaching of the anode[indium-tin oxide (ITO)] by the electron holes and at the same timeblock the transport of electrons, thus improving the collection ofcharges by the anode and inhibiting the recombination phenomena, beforecreating the active layer starting from the mixture of the electronacceptor compound and the electron donor compound as described above, alayer starting from an aqueous suspension comprising PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] is deposited,using suitable deposition techniques such as, for example, spin-coating,spray-coating, ink-jet printing, slot die coating, gravure printing,screen printing, and the like.

More details regarding the different deposition techniques can be found,for example, in Krebs F. C., in “Solar Energy Materials & Solar Cells”(2009), Vol. 93, pg. 394-412.

Inverted polymer photovoltaic cell (or solar cell), generally reportedin literature, comprise, on the other hand, the following layers: (i) asupport in transparent material; (ii) an indium tin oxide (ITO) cathode;(iii) a cathodic buffer layer which acts as an electron carrier and as abarrier to electron holes generally comprising zinc oxide; (iv) anactive layer comprising an electron donor compound and an electronacceptor compound generally selected from those reported above; (v) ananodic interlayer (buffer layer) which acts as a carrier of electronholes and as an electron barrier including a hole transporting material,generally selected from molybdenum oxide, tungsten oxide, vanadiumoxide, (vi) an anode, generally, of silver (Ag), gold (Au) or aluminum(Al).

Generally, in order to protect said polymeric photovoltaic cells (orsolar cells), both with traditional architecture and with invertedstructure, from mechanical stresses and atmospheric agents, and fortheir use in real conditions, said photovoltaic cells (or solar cells)are encapsulated in a suitable material [for example, hybrid multilayerfilms based on poly(ethylene terephthalate), inorganic oxides].

Generally, the aforementioned anodic interlayer (buffer layer) isobtained through a deposition process of molybdenum oxide (or,alternatively, of tungsten or vanadium oxide) carried out by evaporationunder vacuum of said molybdenum oxide, at high temperature and underhigh vacuum (for example, 10⁻⁵ mm Hg-10⁻⁷ mm Hg). However, saiddeposition process has some drawbacks such as, for example: long timesas it is necessary to bring the deposition chamber to the requiredpressures and it takes sufficient time to reach the thickness ofmaterial necessary for the operation of the final photovoltaic (or solarcell) and, consequently, a lengthening of process times and an increasein process costs; high energy consumption; significant waste of materialmainly due to the fact that the oxide vapors fill the deposition chamberand are uniformly deposited on a much larger surface than is actuallyneeded, corresponding to the final photovoltaic cell (or solar cell).

In order for the aforementioned inverted polymer photovoltaic cells (orsolar cells) to find industrial application on a large scale, it istherefore necessary that suitable production processes be developed,capable of overcoming the aforementioned drawbacks. Efforts havetherefore been made in this direction.

For example, Vdlimaki M. et al., in “Nanoscale” (2015), Vol. 7, pg.9570-9580, describe a process for the manufacture of organicphotovoltaic (OPV) modules with inverted structure through roll-to-roll(R2R) molding using the following deposition techniques: gravureprinting and rotary screen-printing. In said inverted structure organicphotovoltaic (OPV) modules the anodic interlayer (buffer layer) includesPEDOT:PSS [poly(3,4-ethylenedioxy-thiophene):polystyrene sulfonate] andis obtained by rotary screen-printing.

However, as reported, for example by Dkhil S. B. et al., in “AdvancedEnergy Materials” (2016), Vol. 6, 1600290, the use of anodic interlayer(buffer layers) comprising materials other than molybdenum oxidegenerally causes a reduction in the efficiencies of the obtained organicsolar cells: in fact, organic solar cells wherein the anodic interlayer(buffer layer) is obtained by means of a molybdenum oxide depositionprocess carried out by vacuum evaporation of said molybdenum oxide, canreach efficiencies higher than 9%.

Furthermore, the use of PEDOT:PSS[poly(3,4-ethylenedioxy-thiophene):polystyrene sulfonate], generally inaqueous suspension or in mixed water/alcohol solvents, as a material forthe anodic interlayer (buffer layer), has some drawbacks from apractical point of view, known to those skilled in the art. The firstdrawback is represented by the strong acidity of the solution used whichgenerally has a pH equal to 2 or 3, which determines a long-terminstability of the polymeric photovoltaic cells (or solar cells), causedby the gradual corrosion of the anode with which said anodic interlayer(buffer layer) is in contact, or with the cathode, following the slowdiffusion of the H⁺ ions through the active layer. A second drawback isrepresented by the fact that the aqueous suspension has very poorwettability properties towards the active layer: this causes an unevencovering of the layer itself and therefore a reduction in theeffectiveness of the anodic interlayer (buffer layer) in acting by layerof carrier of electron holes. It is possible to overcome this drawbackby modifying said suspension with the addition of suitable surfactants,but this determines, on the one hand, an increase in the cost of thematerial, and on the other a decrease in the conductivity of said anodicinterlayer (buffer layer), as the surfactants act as electricalinsulators.

Therefore, the use of PEDOT:PSS[poly(3,4-ethylenedioxy-thiophene):polystyrene sulfonate], is not anoptimal solution in the manufacture of polymeric photovoltaic cells (orsolar cells) and it is therefore of great interest to identifyalternative routes.

Among the soluble materials alternative to PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] proposed by thescientific community we can cite, for example, the soluble derivativesof molybdenum or vanadium. For example, Xu M.-F. et al., in “OrganicElectronics” (2013), Vol. 14, pg. 657-664, describe the use of anaqueous solution of molybdenum oxide (MoO₃) in order to create an anodicinterlayer (buffer layer) in conventional dispersed heterojunction (bulkheterojunction) organic solar cells [comprising poly(3-hexylthiophene)(P3HT) and fullerene]. However, this solution cannot be used in invertedorganic solar cells, as said aqueous solution would not be able toadequately wet the active layer.

Liu J. et al., in “Journal of Materials Chemistry C” (2014), Vol. 2, pg.158-163, describe the use of a solution of molybdenum oxide (MoO₃) inammonia-water in order to create an anodic interlayer (buffer layer)which is deposited on the anode [indium-tin oxide (ITO)] by spin-coatingand subsequently subjected to a thermal treatment (annealing) at 150° C.for 20 minutes. Also said solution is used in conventional dispersedheterojunction (bulk heterojunction) organic solar cells [includingpoly(3-hexylthiophene) (P3HT) and fullerene] and cannot be used ininverted organic solar cells due to the same drawbacks above described.Furthermore, the aforementioned thermal treatment (annealing) is carriedout at a temperature that is not compatible with the use of flexibleplastic supports and takes a too long time for a high-speed depositionprocess (10 m-50 m per minute).

Murase S. et al., in “Advanced Materials” (2012), Vol. 24, pg.2459-2462, describe the use of a MoO₃ solution obtained by thermaldecomposition, in deionized water, of ammonium heptamolybdate asprecursor, in order to create an anodic interlayer (buffer layer) whichis deposited on the anode [indium-tin oxide (ITO)] by spin-coating. Alsoin this case the solution is used in conventional organic solar cells(i.e. not with inverted structure) due to the wettability problems ofthe active layer.

Hammond S. R. et al., in “Journal of Materials Chemistry” (2012), Vol.22, pg. 3249-3254, describe the use of a molybdenum oxide (MoO_(x))solution obtained by thermal decomposition, in acetonitrile, ofmolybdenum tricarbonyl trispropionitrile as precursor, in order tocreate an anodic interlayer (buffer layer) which is deposited on theanode [indium-tin oxide (ITO)] by spin-coating. The acetonitrilesolution of molybdenum tricarbonyl trispropionitrile is prepared in aninert atmosphere due to the instability of said precursor. Saidinstability, the very high cost of the precursor and the known toxicityof the metal-carbonyl derivatives, make the process described thereinunsuitable for use in a large-scale industrial process.

Zilberg K. et al., in “Applied Materials & Interfaces” (2012), Vol. 4,pg. 1164-1168, describe the use of a MoO_(x) solution obtained bythermal decomposition, in iso-propanol (containing about 0.1% water), ofbis(2,4-pentandionate)molybdenum (IV) dioxide as precursor, in order tocreate an anodic interlayer (buffer layer) which is deposited on theanode (Ag) by spin-coating and is subsequently subjected to a thermaltreatment (annealing) at 110° C., for 1 hour. These times are completelyincompatible with a high speed deposition process (10 m-50 m perminute).

Zhu Y. et al., in “Journal o fMaterials Chemistry A” (2014), Vol. 2, pg.1436-1442, describe the use of a solution of phosphomolybdic acid (PMA),in iso-propanol, in order to create an anodic interlayer (buffer layer)which is deposited on the anode (Ag) by spin-coating and subsequently itis subjected to a thermal treatment (annealing) at 150° C., for 90minutes. The inverted organic solar cells comprising said interlayer aresaid to have efficiencies comparable or slightly higher than those ofthe inverted solar cells comprising an anodic interlayer (buffer layer)obtained through a molybdenum oxide deposition process carried out byevaporation of said molybdenum oxide. However, the long times of saidthermal treatment are not compatible with roll-to-roll (R2R) moldingprocess.

Chinese patent application CN103400941 relates to an organic solar cellbased on a modified anodic layer comprising: a cathode, a modifiedcathodic interlayer (buffer layer), one active layer with dispersedheterojunction (bulk heterojunction), a modified anodic interlayer(buffer layer) and an anode; where said modified anodic interlayer(buffer layer) is based on a heteropolyacid having formulaH_(x)(MM′₁₂OR₄₀) wherein M is phosphorus (P) or silicon (Si), M′ ismolybdenum (Mo) or tungsten (W), X is 3 or 4; the cathode is indium tinoxide (ITO); the modified anodic interlayer (buffer layer) is zincoxide; the active layer with bulk heterojunction is a mixture compoundssuch as poly(3-hexylthiophene) (P3HT) and fullerenes; the anode issilver or aluminum.

Vasilopoulou M. et al., in “Journal of the American Chemical Society”(2015), Vol. 137 (21), pg. 6844-6856, describe the use of Keggin andDawson-type polyoxymetallates (POMs) as cathodic interlayers (bufferlayers) in high efficiency optoelectronic devices. Said cathodic bufferlayers have the function of electron transport materials and holeblockers.

Kim J.-H. et al., in “Electronic Materials Letters” (2016), Vol. 12, No.3, pg. 383-387, describe an inverted organic solar cell based onP3HT:PCBM having an improved charge transport thanks to the use ofmolybdenum oxide nanoparticles (MoO₃ NPs) as a hole transportinginterlayer positioned between the active layer P3HT:PCBM and the anodicinterlayer of PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrenesulfonate]. Said organic solar cell has a photoelectric conversionefficiency (power conversion efficiency—PCE) (η) equal to 4.11% higherthan that of an organic solar cell without the aforementioned holetransporting interlayer of molybdenum oxide nanoparticles (MoO₃ NPs)which is, in fact, equal to 3.70%.

The Applicant has noted that, in addition to the aforementioneddrawbacks, the adhesion between the different layers of the invertedpolymer photovoltaic cells (or solar cells) and, in particular, theadhesion between the active layer and the anodic interlayer (bufferlayer), it is often poor.

Consequently, the Applicant faced the problem of finding an invertedpolymer photovoltaic cell (or solar cell) having good performance and agood level of adhesion between the different layers, more particularlybetween the active layer and the anodic interlayer (buffer layer) whilemaintaining good values of photoelectric conversion efficiency (powerconversion efficiency—PCE) (η).

SUMMARY

The Applicant has now found that the use of a first anodic interlayer(buffer layer) based on PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] and of a secondanodic interlayer (buffer layer), wherein said second anodic interlayer(buffer layer) comprises at least one heteropolyacid and, optionally, atleast one amino compound, allows to obtain an inverted polymerphotovoltaic cell (or solar cell) having good performance. Inparticular, the Applicant has now found that the use of said firstanodic interlayer (buffer layer) and second anodic interlayer (bufferlayer), allows to obtain an inverted polymer photovoltaic cell (or solarcell) having not only good values of photoelectric conversion efficiency(power conversion efficiency—PCE) (η) but also a good level of adhesionbetween the different layers, more in particular between the activelayer and said first anodic interlayer (buffer layer).

Therefore, the present disclosure provides an inverted polymerphotovoltaic cell (or solar cell) comprising:

-   -   an anode;    -   a first anodic interlayer (buffer layer) based on PEDOT:PSS        [poly(3,4-ethylenedioxythiophene):polystyrene sulfonate];    -   an active layer comprising at least one photoactive organic        polymer as an electron donor and at least one electron acceptor        organic compound;    -   a cathodic interlayer (buffer layer);    -   a cathode;    -   wherein a second anodic interlayer (buffer layer) comprising at        least one heteropolyacid and, optionally, at least one amino        compound is placed between said first anodic interlayer (buffer        layer) and said active layer.

For the purpose of the present description and of the following claims,the definitions of the numerical ranges always include the extremesunless otherwise specified.

For the purpose of the present description and of the following claims,the terms first anodic interlayer (buffer layer) and second anodicinterlayer (buffer layer) are to be understood as indicated as a simpleorder of description and not as an order of deposition during theprocess for the preparation of said inverted polymer photovoltaic cell(or solar cell) described below.

In accordance with a preferred embodiment of the present disclosure,said anode can be made of a metal, said metal being preferably selected,for example, from silver (Ag), gold (Au), aluminum (Al); or it canconsist of grids in conductive material, said conductive material beingpreferably selected, for example, from silver (Ag), copper (Cu),graphite, graphene, and of a transparent conductive polymer, saidtransparent conductive polymer being, preferably, PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; or it canconsist of an ink based on metal nanowires, said metal being preferablyselected, for example, from silver (Ag), copper (Cu).

Said anode can be obtained by depositing said metal on top of said firstanodic interlayer (buffer layer) through the deposition techniques knownin the art such as, for example, vacuum evaporation, flexographicprinting, knife-over-edge-coating, spray-coating, screen-printing.Alternatively, said anode can be obtained by depositing, above saidfirst anodic interlayer (buffer layer), said transparent conductivepolymer via spin coating, or gravure printing, or flexographic printing,or slot die coating, followed by deposition of said grids in conductivematerial via evaporation, or screen-printing, or spray-coating, orflexographic printing. Alternatively, said anode can be obtained bydepositing, above said first anodic interlayer (buffer layer), of saidink based on metal nanowires via spin coating, or gravure printing, orflexographic printing, or slot die coating.

Dispersions or solutions of PEDOT:PSS[poly(3,4-ethylenedioxy-thiophene):polystyrene sulfonate] which can beadvantageously used for the purpose of the present disclosure and whichare currently commercially available are the products Clevios™ fromHeraeus, Orgacon™ from Agfa.

In order to improve the deposition and the properties of said firstanodic interlayer (buffer layer), one or more additives can be added tosaid dispersions or solutions, such as, for example: polar solvents suchas, for example, alcohols (for example, methanol, ethanol, propanol),dimethyl sulfoxide, or mixtures thereof; anionic surfactants such as,for example, carboxylates, suifonated α-olefins, sulfonated alkylbenzenes, alkyl sulfonates, esters of alkyl ether sulfonates,triethanolamines alkyl sulfonates, or mixtures thereof; cationicsurfactants such as, for example, alkyltrimethylammonium salts,dialkyldimethylammonium chlorides, alkylpyridinium chlorides, ormixtures thereof; ampholytic surfactants such as, for example,alkylcarboxybetaines, or mixtures thereof; non-ionic surfactants suchas, for example, carboxylic diethanolamides, polyoxyethylene alkylethers, polyoxyethylene alkyl phenyl ethers, or mixtures thereof; polarcompounds (for example, imidazole), or mixtures thereof; or mixturesthereof. More details regarding the addition of said additives can befound, for example, in: Synooka O. et al., “ACS AppliedMaterials &Interfaces” (2014), Vol. 6 (14), pg. 11068-11081; Fang G. et al.,“Macromolecular Chemistry and Physics” (2011), Vol. 12, Issue 17, pg.1846-1851.

Said first anodic interlayer (buffer layer) can be obtained bydepositing the PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrenesulfonate], in the form of dispersion or solution, above the anodethrough the deposition techniques known in the art such as, for example,vacuum evaporation, spin coating, drop casting, doctor blade casting,slot die coating, gravure printing, flexographic printing,knife-over-edge-coating, spray-coating, and screen-printing.

According to a preferred embodiment of the present disclosure, saidphotoactive organic polymer can be selected, for example, from:

-   -   (a) polythiophenes such as, for example, regioregular        poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene),        poly(3,4-ethylenedioxythiophene), or mixtures thereof;    -   (b) alternating or statistical conjugated copolymers comprising:        -   at least one benzotriazole (B) unit having general formula            (Ia) or (Ib):

-   -   -   wherein group R is selected from alkyl groups, aryl groups,            acyl groups, thioacyl groups, said alkyl, aryl, acyl and            thioacyl groups being optionally substituted;        -   at least one conjugate structural unit (A), wherein each            unit (B) is connected to at least one unit (A) in any one of            the positions 4, 5, 6, or 7, preferably in the positions 4            or 7;

    -   (c) alternating conjugated copolymers comprising        benzothiadiazole units such as, for example, PCDTBT        {poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]},        PCPDTBT        {poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]};

    -   (d) alternating conjugated copolymers comprising        thieno[3,4-b]pyrazidine units;

    -   (e) alternating conjugated copolymers comprising quinoxaline        units;

    -   (f) alternating conjugated copolymers comprising monomer silol        units such as, for example, copolymers of        9,9-dialkyl-9-silafluorene;

    -   (g) alternating conjugated copolymers comprising condensed        thiophene units such as, for example, copolymers of        thieno[3,4-b]thiophene and of benzo[1,2-b: 4,5-b′]dithiophene;

    -   (h) alternating conjugated copolymers comprising        benzothiadiazole or naphthothiadiazole units substituted with at        least one fluorine atom and thiophene units substituted with at        least one fluorine atom such as, for example, PffBT4T-2OD        {poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)]},        PBTff4T-2OD        {poly[(2,1,3-benzothiadiazole-4,7-diyl)-alt-4′,3″-difluoro-3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophene-5,5′″-diyl)]},        PNT4T-2OD        {poly(naphtho[1,2-c:5,-c′]bis[1,2,5]thiadiazole-5,10-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;        5″,2′″-quaterthiophene-5,5′″-diyl)]};

    -   (i) conjugated copolymers comprising        thieno[3,4-c]pyrrole-4,6-dione units such as, for example,        PBDTTPD        {poly[[5-(2-ethylhexyl)-5,6-dihydro-4,6-dioxo-4H-thieno[3,4-c]pyrrole-1,3-diyl)[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]};

    -   (l) conjugated copolymers comprising thienothiophene units such        as, for example, PTB7        {poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]},        PBDB-T polymer        {poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]-2,5-thiophenediyl]};

    -   (m) polymers comprising a derivative of indacen-4-one having        general formula (III), (IV) or (V):

-   -   wherein:        -   W and W₁, identical to or different from each other,            preferably identical to each other, represent an oxygen            atom; a sulfur atom; an N—R₃ group wherein R₃ represents a            hydrogen atom, or is selected from C₁-C₂₀, preferably            C₂-C₁₀, linear or branched alkyl groups;        -   Z and Y, identical to or different from each other,            preferably identical to each other, represent a nitrogen            atom; or a C—R₄ group wherein R₄ represents a hydrogen atom,            or is selected from C₁-C₂₀, preferably C₂-C₁₀, linear or            branched alkyl groups, optionally substituted cycloalkyl            groups, optionally substituted aryl groups, optionally            substituted heteroaryl groups, C₁-C₂₀, preferably C₂-C₁₀,            linear or branched alkoxy groups, polyethyleneoxylic groups            R₅—O—[CH₂—CH₂—O]_(n)— wherein R₅ is selected from C₁-C₂₀,            preferably C₂-C₁₀, linear or branched alkyl groups, and n is            an integer between 1 and 4, —R₆—OR₇ groups wherein R₆ is            selected from C₁-C₂₀, preferably C₂-C₁₀, linear or branched            alkylene groups and R₇ represents a hydrogen atom or is            selected from C₁-C₂₀, preferably C₂-C₁₀, linear or branched            alkyl groups, or is selected from polyethyleneoxylic groups            R₅—[—OCH₂—CH₂—]_(n)— wherein R₅ has the same meanings            reported above and n is an integer between 1 and 4, —COR₈            groups wherein R₆ is selected from C₁-C₂₀, preferably            C₂-C₁₀, linear or branched alkyl groups, —COOR₉ groups            wherein R₉ is selected from C₁-C₂₀, preferably C₂-C₁₀,            linear or branched alkyl groups; or they represent a —CHO            group, or a cyano group (—CN);    -   R₁ and R₂, identical to or different from each other, preferably        identical to each other, are selected from C₁-C₂₀, preferably        C₂-C₁₀, linear or branched alkyl groups; optionally substituted        cycloalkyl groups; optionally substituted aryl groups;        optionally substituted heteroaryl groups; C₁-C₂₀, preferably        C₂-C₁₀, linear or branched alkoxy groups; polyethyleneoxylic        groups R₅—O—[CH₂—CH₂—O]_(n)— wherein R₅ has the same meanings        reported above and n is an integer between 1 and 4; groups        —R₆—OR₇ wherein R₆ and R₇ have the same meanings reported above;        —COR₈ groups wherein R₈ has the same meanings reported above;        —COOR₉ groups wherein R₉ has the same meanings reported above;        or they represent a —CHO group, or a cyano group (—CN);        -   D represents an electron donor group;        -   A represents an electron acceptor group;        -   n is an integer between 10 and 500, preferably between 20            and 300;    -   (n) polymers comprising antradithiophene derivatives having        general formula (X)

-   -   -   wherein:            -   Z, identical to or different from each other, preferably                identical to each other, represent a sulfur atom, an                oxygen atom, a selenium atom;            -   Y, identical to or different from each other, preferably                identical to each other, represent a sulfur atom, an                oxygen atom, a selenium atom;            -   R₁, identical or different from each other, preferably                identical to each other, are selected from amino groups                —N—R₃R₄ wherein R₃ represents a hydrogen atom, or is                selected from C₁-C₂₀, preferably C₂-C₁₀, linear or                branched alkyl groups, or is selected from optionally                substituted cycloalkyl groups and R₄ is selected from                C₁-C₂₀, preferably C₂-C₁₀, linear or branched alkyl                groups, or is selected from optionally substituted                cycloalkyl groups; or are selected from C₁-C₃₀,                preferably C₂-C₂₀, linear or branched alkoxy groups; or                are selected from polyethyleneoxylic groups                R₅—O—[CH₂—CH₂—O]_(n)— wherein R₅ is selected from                C₁-C₂₀, preferably C₂-C₁₀, linear or branched alkyl                groups, and n is an integer between 1 and 4; or are                selected from —R₆—OR₇ groups wherein R₆ is selected from                C₁-C₂₀, preferably C₂-C₁₀, linear or branched alkylene                groups and R₇ represents a hydrogen atom, or is selected                from C₁-C₂₀, preferably C₂-C₁₀, linear or branched alkyl                groups, or is selected from polyethyleneoxyl groups                R₅—[—OCH₂—CH₂—]_(n)— wherein R₅ has the same meanings                reported above and n is an integer between 1 and 4; or                are selected from thiol groups —S—R₈ wherein R₈ is                selected from C₁-C₂₀, preferably C₂-C₁₀, linear or                branched alkyl groups;            -   R₂, identical to or different from each other,                preferably identical to each other, represent a hydrogen                atom; or are selected from C₁-C₂₀, preferably C₂-C₁₀,                linear or branched alkyl groups; or are selected from                —COR₉ groups wherein R₉ is selected from C₁-C₂₀,                preferably C₂-C₁₀, linear or branched alkyl groups; or                are selected from —COOR₁₀ groups wherein R₁₀ is selected                from C₁-C₂₀, preferably C₂-C₁₀, linear or branched alkyl                groups; or are selected from optionally substituted aryl                groups; or are selected from optionally substituted                heteroaryl groups;        -   A represents an electron acceptor group;        -   n is an integer between 10 and 500, preferably between 20            and 300.

More details related to alternating or statistical conjugated copolymers(b) comprising at least one benzotriazole unit (B) and at least oneconjugated structural unit (A) and the process for their preparation canbe found, for example, in the international patent application WO2010/046114 in the name of the Applicant.

More details related to alternating conjugated copolymers comprisingbenzothiodiazoles units (c), alternating conjugated copolymerscomprising thieno [3,4-b]pyrazidine units (d), alternating conjugatedcopolymers comprising quinoxaline units (e), alternating conjugatedcopolymers comprising silol monomer units (f), alternating conjugatedcopolymers comprising thiophene condensate units (g), can be found, forexample, in Chen J. et al., Accounts of chemical research (2009), Vol.42, No. 11, pg. 1709-1718; Po' R. et al., “Macromolecules” (2015), Vol.48 (3), pg. 453-461.

More details related to alternating conjugated copolymers comprisingbenzothiodiazole or naphthothiadiazole units substituted with at leastone fluorine atom and thiophene units substituted with at least onefluorine atom (h) can be found, for example, in Liu Y. et al., “NatureCommunications” (2014), Vol. 5, Paper no. 5293 (DOI:10.1038/ncomms6293).

More details related to conjugated copolymers comprisingthieno[3,4-c]pyrrole-4,6-dione units (i) can be found, for example, inPan H. et al, “Chinese Chemical Letters” (2016), Vol 27, Issue 8, pg.1277-1282.

More details related to conjugated copolymers comprising thienothiopheneunits (1) can be found, for example, in Liang Y. et al., “Journal of theAmerican Chemical Society” (2009), Vol. 131 (22), pg. 7792-7799; LiangY. et al., “Accounts of Chemical Research” (2010), Vol. 43 (9), pg.1227-1236.

More details related to polymers comprising a derivative ofindacen-4-one (m) can be found, for example, in the international patentapplication WO 2016/180988 in the name of the Applicant.

More related details to polymers comprising antradithiophene derivativeshaving general formula (X) (n) can be found, for example, in theinternational patent application WO 2019/175367 in the name of theApplicant.

In accordance with a particularly preferred embodiment of the presentdisclosure, said photoactive organic polymer can be selected, forexample, from PffBT4T-2OD {poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)]},PBDTTPD{poly[[5-(2-ethylhexyl)-5,6-dihydro-4,6-dioxo-4H-thieno[3,4-c]pyrrole-1,3-diyl)[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]},PTB7 {poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[11,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]},PBDB-T{poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]},polymers comprising antradithiophene derivatives having general formula(X). Polymers comprising antradithiophene derivatives having generalformula (X) are preferred.

In accordance with a preferred embodiment of the present disclosure,said organic electron acceptor compound can be selected, for example,from derivatives of fullerene such as, for example,[6,6]-phenyl-Ci-butyric acid methyl ester (PCBM),[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), indene-C₆₀bis-adduct (ICBA), bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C₆₂(Bis-PCBM). [6,6]-Phenyl-C₆₁-butyric acid methyl ester (PCBM),[6,6]-Phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), are preferred.

In accordance with a further preferred embodiment of the presentdisclosure, said organic electron acceptor compound can be selected, forexample, from non-fullerene compounds, optionally polymeric, such as,for example, compounds based on perylene-diimides ornaphthalene-diimides and fused aromatic rings; indacenothiophenes withelectron-poor terminal groups; compounds having an aromatic core capableof symmetrically rotating, for example, derivatives of corannulene ortruxenone.3,9-Bis{2-methylene-[3-(1,1-dicyanomethylene)-indanone]}-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3‘-d’]-s-indacene[1,2-b:5,6-b′]-dithiophene,poly{[N,N-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)},are preferred.

More details relating to said non-fullerene compounds can be found, forexample, in Nielsen C. B. et al., “Accounts of Chemical Research”(2015), Vol. 48, pg. 2803-2812; Zhan C. et al, “RSC Advances” (2015),Vol. 5, pg. 93002-93026.

Said active layer can be obtained by depositing, above said cathodicinterlayer (buffer layer), a solution comprising at least onephotoactive organic polymer and at least one organic electron acceptorcompound, selected from those reported above, using suitable depositiontechniques such as, for example, spin-coating, spray-coating, ink-jetprinting, slot die coating, gravure printing, screen printing.

According to a preferred embodiment of the present disclosure, saidcathodic interlayer (buffer layer) can comprise zinc oxide, titaniumoxide, preferably zinc oxide.

Said cathodic interlayer (buffer layer) can be obtained by depositing aprecursor solution of zinc oxide on said cathode by means of depositiontechniques known in the art such as, for example, vacuum evaporation,spin-coating, drop casting, doctor blade casting, slot die coating,gravure printing, flexographic printing, knife-over-edge-coating,spray-coating, screen-printing.

More details in relation to the formation of said cathodic interlayer(buffer layer) starting from a precursor solution of zinc oxide can befound, for example, in Pó R. et al., “Energy & Environmental Science”(2014), Vol. 7, pg. 925-943.

According to a preferred embodiment of the present disclosure, saidcathode can be of a material selected, for example, from: indium-tinoxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide doped withaluminum (AZO), zinc oxide doped with gadolinium oxide (GZO); or it canconsist of grids in conductive material, said conductive material beingpreferably selected, for example, from silver (Ag), copper (Cu),graphite, graphene, and a of transparent conductive polymer, saidtransparent conductive polymer being, preferably, PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; or it canconsist of an ink based on metal nanowires, said metal being preferablyselected, for example, from silver (Ag), copper (Cu).

Said cathode can be obtained by means of techniques known in the artsuch as, for example, sputtering, electron beam assisted deposition.Alternatively, said cathode can be obtained by depositing saidtransparent conductive polymer via spin coating, or gravure printing, orflexographic printing, or slot die coating, preceded by the depositionof said grids in conductive material via evaporation, orscreen-printing, or spray-coating, or flexographic printing.Alternatively, said cathode can be obtained by depositing said ink basedon metal nanowires via spin coating, or gravure printing, orflexographic printing, or slot die coating. The deposition can takeplace on the support layer selected from those reported below.

In accordance with a preferred embodiment of the present disclosure,said cathode can be associated with a support layer which can be oftransparent rigid material such as, for example, glass, or of flexiblematerial such as, for example, polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyethylene imine (PI), polycarbonate(PC), polypropylene (PP), polyimide (PI), triacetyl cellulose (TAC), orcopolymers thereof.

In accordance with a preferred embodiment of the present disclosure,said at least one heteropolyacid can be selected, for example, fromheteropolyacids having general formula (I):

H_(x)[A(MO₃)_(y)O_(z)]  (I)

wherein:

-   -   A represents a silicon atom, or a phosphorus atom;    -   M represents an atom of a transition metal belonging to group 5        or 6 of the Periodic Table of the Elements, preferably selected        from molybdenum, tungsten;    -   x is an integer that depends on the valence of A, preferably is        3 or 4;    -   y is 12 or 18;    -   z is 4 or 6.

In accordance with a further preferred embodiment of the presentdisclosure, said at least one heteropolyacid can be selected, forexample, from heteropolyacids having general formula (II):

H_(x)[A(Mo)_(p)(V)_(q)O₄₀]  (II)

wherein:

-   -   A represents a silicon atom, or a phosphorus atom;    -   x is an integer that depends on the valence di A, preferably is        3 or 4;    -   p is 6 or 10;    -   q is 2 or 6.

For the purpose of the present disclosure, said heteropolyacids havinggeneral formula (I) and said heteropolyacids having general formula (II)can be used in hydrated form, or in alcoholic solution (for example, inethanol, iso-propanol, or mixtures thereof).

In accordance with a preferred embodiment of the present disclosure,said heteropolyacids having general formula (I) and said heteropolyacidshaving general formula (II) can be selected, for example, from: hydratedphosphomolybdic acid {H₃[P(MoO₃)₁₂O₄]·nH₂O}, phosphomolybdic acid{H₃[P(MoO₃)₁₂O₄]} in alcoholic solution, hydrated phosphotungstic acid{H₃[P(WO₃)₁₂O₄]·nH₂O}, phosphotungstic acid in alcoholic solution{H₃[P(WO₃)₁₂O₄]}, hydrated silicomolybdic acid {H₄[Si(MoO₃)₁₂O₄]·nH₂O},silicomolybdic acid {H₄[Si(MoO₃)₁₂O₄]} in alcoholic solution, hydratedsilicotungstic acid {H₄[Si(WO₃)₁₂O₄]·nH₂O}, silicotungstic acid{H₄[Si(WO₃)₁₂O₄]} in alcoholic solution, hydrated phosphomolybdovanadicacid {H₃[P(Mo)₆(V)₆O₄₀]·nH₂O}, phosphomolybdovanadic acid{H₃[P(Mo)₆(V)₆O₄₀]} in alcoholic solution, hydratedphosphomolybdovanadic acid {H₃[P(Mo)₁₀(V)₂O₄₀]·nH₂O},phosphomolybdovanadic acid {H₃[P(Mo)₁₀(V)₂O₄₀]} in alcoholic solution ormixtures thereof. Hydrated phosphomolybdic acid {H₃[P(MoO₃)₁₂O₄]·nH₂O},phosphomolybdic acid {H₃[P(MoO₃)₁₂O₄]} in alcoholic solution, hydratedsilicotungstic acid {H₄[Si(WO₃)₁₂O₄]·nH₂O}, are preferred.

Heteropolyacids having general formula (I) or (II) are commerciallyavailable, or they can be prepared according to processes known in theart as described, for example, in American patents U.S. Pat. Nos.4,146,574 and 5,792,721, or by Odyakov V. F. et al., in “AppliedCatalysis A General” (2008), Vol. 342 (1), pg. 126-130.

In accordance with a preferred embodiment of the present disclosure,said amino compound can be selected, for example, from:

-   -   low molecular weight aliphatic amines, containing from 8 to 24        carbon atoms, linear or branched, primary, secondary or        tertiary, such as, for example, n-octylamine, n-dodecylamine,        n-hexadecylamine, di-n-octylamine, or mixture thereof;    -   conjugated polymers containing chain or side amino groups such        as, for example, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]        (PTAA), poly(N,N-bis-4-butylphenyl-N,N-bisphenyl)benzidine        (polyTPD),        poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)]        (PFN), or mixtures thereof,    -   or mixtures thereof.

Said second anodic interlayer (buffer layer) can be obtained bydepositing an alcoholic solution of said at least one heteropolyacid ontop of the active layer, by means of deposition techniques known in theart such as, for example, vacuum evaporation, spin coating, dropcasting, doctor blade casting, slot die coating, gravure printing,flexographic printing, knife-over-edge-coating, spray-coating,screen-printing, adjusting from time to time the rheological parametersof said at least one heteropolyacid in the form of a solution (forexample, viscosity) according to the requirements of the depositiontechnique used.

In the event that said second anodic interlayer (buffer layer) alsocomprises at least one amino compound, said second interlayer (bufferlayer) can also be obtained by depositing a solution of said at leastone heteropolyacid and said at least one amino compound, in an etherealsolvent such as, for example, tetrahydrofuran, dioxane, or in ahydrocarbon solvent such as, for example, xylene, toluene, operating asdescribed above in the case of an alcoholic solution of said at leastone heteropolyacid.

As mentioned above, the anode, the cathode, the first anodic interlayer(buffer layer), the second anodic interlayer (buffer layer) and thecathodic interlayer (buffer layer) present in the aforementionedinverted polymer photovoltaic cell (or solar cell), can be deposited bymeans of techniques known in the art. More details regarding thesetechniques can be found, for example in: Pó R. et al., “InterfacialLayers”, in “Organic Solar Cells—Fundamentals, Devices, and Upscaling”(2014), Chapter 4, Richter H. and Rand B. Eds., Pan Stanford PublishingPte Ltd.; Yoo S. et al, “Electrodes in Organic Photovoltaic Cells,” in“Organic Solar Cells—Fundamentals, Devices, and Upscaling” (2014),Chapter 5, Richter H. and Rand B. Eds., Pan Stanford Publishing PteLtd.; Angmo D. et al., “Journal of Applied Polymer Science” (2013), Vol.129, Issue 1, pg. 1-14.

As stated above, the present disclosure also relates to a process forthe preparation of the aforementioned inverted polymer photovoltaic cell(or solar cell).

In accordance with a preferred embodiment of the present disclosure, theprocess for the preparation of the inverted polymer photovoltaic cell(or solar cell) comprises:

-   -   forming the cathode by sputtering; or by electron beam assisted        deposition; or by depositing a transparent conductive polymer        via spin coating, or gravure printing, or flexographic printing,        or slot die coating, preceded by deposition of grids in        conductive material via evaporation, or screen-printing, or        spray-coating, or flexographic printing; or by depositing an ink        based on metal nanowires via spin coating, or gravure printing,        or flexographic printing, or slot die coating;    -   forming the cathodic interlayer (buffer layer) by spin coating,        or gravure printing, or flexographic printing, or slot die        coating above said cathode;    -   forming the active layer by spin coating, or gravure printing,        or slot-die coating, above said cathodic interlayer (buffer        layer);    -   forming the second anodic interlayer (buffer layer) by spin        coating, or gravure printing, or screen-printing, or        flexographic printing, or slot-die coating above said active        layer;    -   forming the first anodic interlayer (buffer layer) by spin        coating, or gravure printing, or screen-printing, or        flexographic printing, or slot-die coating, above said second        anodic interlayer (buffer layer);    -   forming the anode by vacuum evaporation, or screen-printing, or        spray-coating, or flexographic printing, above said first anodic        interlayer (buffer layer); or by deposition of a transparent        conductive polymer via spin coating, or gravure printing, or        flexographic printing, or slot die coating, followed by        deposition of grids in conductive material via evaporation, or        screen-printing, or spray-coating, or flexographic printing,        above said first anodic interlayer (buffer layer); or by        deposition of an ink based on metal nanowires via spin coating,        or gravure printing, or flexographic printing, or slot die        coating, above said first anodic interlayer (buffer layer).

In accordance with a preferred embodiment of the present disclosure, inthe inverted polymer photovoltaic cell (or solar cell) object of thepresent disclosure:

-   -   the anode can have a thickness ranging between 50 nm and 150 nm,        preferably ranging between 80 nm and 120 nm;    -   the first anodic interlayer (buffer layer) can have a thickness        ranging between 10 nm and 2000 nm, preferably ranging between 15        nm and 1000 nm;    -   the second anodic interlayer (buffer layer) can have a thickness        ranging between 1 nm and 100 nm, preferably ranging between 2 nm        and 40 nm;    -   the active layer can have a thickness ranging between 50 nm and        500 nm, preferably ranging between 70 nm and 360 nm;    -   the cathodic interlayer (buffer layer) can have a thickness        ranging between 10 nm and 100 nm, preferably ranging between 20        nm and 80 nm;    -   the cathode can have a thickness ranging between 50 nm and 150        nm, preferably ranging between 80 nm and 120 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be illustrated in greater detail throughan embodiment with reference to FIG. 1 below reported which represents across-sectional view of an inverted polymer photovoltaic cell (or solarcell) object of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWING AND DISCLOSURE

With reference to FIG. 1 , the inverted polymer photovoltaic cell (orsolar cell) (1) comprises:

-   -   a transparent support (7), for example, a glass or plastic        support;    -   a cathode (2), for example an indium tin oxide (ITO) cathode; or        a cathode obtained by depositing a transparent conductive        polymer via spin coating, or gravure printing, or flexographic        printing, or slot die coating, preceded by deposition of grids        in conductive material via evaporation, or screen-printing, or        spray-coating, or flexographic printing; or a cathode obtained        by depositing an ink based on metal nanowires via spin coating,        or gravure printing, or flexographic printing, or slot die        coating;    -   a cathodic interlayer (buffer layer) (3), comprising, for        example, zinc oxide;    -   a layer of photoactive material (4) comprising at least one        photoactive organic polymer, for example, a polymer comprising        antradithiophene derivatives having general formula (X) (for        example copolymer having formula (Xb) below reported), and at        least one derivative of fullerene, for example,        [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), or at least        one non-fullerene compound, optionally polymeric;    -   a second anodic interlayer (buffer layer) (5 b), comprising an        alcohol solution of at least one heteropolyacid having general        formula (I) or (II) above reported, for example, phosphomolybdic        acid trihydrate; or an alcoholic solution of at least one        heteropolyacid having general formula (I) or (II) above        reported, for example, phosphomolybdic acid trihydrate and at        least one low molecular weight aliphatic amine, for example        n-dodecylamine; or a solution in tetrahydrofuran of at least one        heteropolyacid having general formula (I) or (II) above        reported, for example, phosphomolybdic acid trihydrate and at        least one conjugated polymer containing chain or side amino        groups, for example,        poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]        (PFN);    -   a first anodic interlayer (buffer layer) (5 a), comprising, for        example, PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrene        sulfonate];    -   an anode (6), for example, a silver (Ag) anode; or an anode        obtained by depositing a transparent conductive polymer via spin        coating, or gravure printing, or flexographic printing, or slot        die coating, followed by deposition of grids in conductive        material via evaporation, or screen-printing, or spray-coating,        or flexographic printing; or an anode obtained by depositing an        ink based on metal nanowires via spin coating, gravure printing,        flexographic printing, or slot die coating.

In order to better understand the present disclosure and to put it intopractice, it is reported below some illustrative and non-limitingexamples of the same.

Example 1 (Disclosure)

SOLAR cell with copolymer (Xb):PC₇₁BM, phosphomolybdic acid andPEDOT:PSS

A polymer-based device was prepared on a substrate of polyethyleneterephthalate (PET) coated with ITO (indium tin oxide) (FomTechnologies—Denmark) (100 nm), previously subjected to a cleaningprocedure with a stream of compressed nitrogen and then, by means of anair plasma device (Diener Electronic GmbH & Co.—Germany), immediatelybefore proceeding to the next step.

The substrate thus treated was ready for the deposition of the cathodicinterlayer (buffer layer). For this purpose, the zinc oxide interlayer(buffer layer) was obtained starting from a 2.6% by weight solution ofzinc oxide nanoparticles (Aldrich) in iso-propanol (Aldrich). Thesolution was deposited, in the air, on the substrate using a slot-dietool (Roller Coater—FOM Technologies—Denmark) operating under thefollowing conditions:

-   -   flow: 30 μl/min;    -   speed of substrate: 0.5 m/min;    -   gap: 50 m.

Immediately after deposition of the cathodic interlayer (buffer layer),the formation of zinc oxide was obtained by treating everythingthermally at 140° C., for 3 minutes, in a ventilated air oven. Thecathodic interlayer (buffer layer) thus obtained had a thickness of 70nm.

A solution of 14 mg/ml of the copolymer having formula (Xb) obtained asdescribed in Example 6 of the international patent application WO2019/175367 above reported and 24.5 mg/ml of [6,6]-phenyl-C₇₁-butyricacid methyl ester (PC₇₁BM) (Nano-C), in o-xylene (Aldrich), wasprepared. The active layer was deposited, in the air, starting from thesolution thus obtained, using a slot-die tool (Roller Coater of FOMTechnologies—Denmark) operating under the following conditions:

-   -   flow: 120 μl/min;    -   speed of substrate: 0.75 m/min;    -   gap: 50 μm.

Immediately after the deposition of the active layer, everything wasthermally treated at 120° C., for 2 minutes, in a ventilated air oven.The active layer thus obtained had a thickness of 300 nm.

Above the active layer thus obtained, the second anodic interlayer(buffer layer) was deposited in the air, starting from a solution ofphosphomolybdic acid trihydrate (Aldrich) in iso-propanol (Aldrich) (6mg/ml) through a slot-die tool (Roller Coater of FOMTechnologies—Denmark) operating under the following conditions:

-   -   flow: 100 μl/min;    -   speed of substrate: 0.75 m/min;    -   gap: 50 μm.

The second anodic interlayer (buffer layer) thus obtained had athickness of 5 nm.

Above said second anodic interlayer (buffer layer), the first anodicinterlayer (buffer layer) was deposited in the air, starting from asuspension comprising PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] (Clevios™ HTLSolar 388—Heraeus Co.) with a concentration of PEDOT:PSS equal to 1.2mg/ml, using a slot-die tool (Roller Coater of FOM Technologies—Denmark)operating under the following conditions:

-   -   flow: 360 μl/min;    -   speed of substrate: 1 m/min;    -   gap: 100 μm.

Immediately after the deposition of the first anodic interlayer (bufferlayer), everything was thermally treated at 120° C., for 2 minutes, in aventilated air oven. The first anodic interlayer (buffer layer) thusobtained had a thickness of 150 nm.

Above said first anodic interlayer (buffer layer) the silver (Ag) anodewas deposited, having a thickness of 100 nm, by vacuum evaporation,suitably masking the area of the device in order to obtain an activearea equal to 0.25 mm².

The deposition of the anode was carried out in a standard vacuumevaporation chamber containing the substrate and an evaporation vesselequipped with a heating element containing 10 silver (Ag) shots(diameter 1 mm-3 mm) (Aldrich). The evaporation process was carried outunder vacuum, at a pressure of about 1×10⁻⁶ bar. The silver (Ag), afterevaporation, was condensed in the non-masked parts of the device.

The thicknesses were measured with a Dektak 150 profilometer (VeecoInstruments Inc.).

Measurement of photoelectric conversion efficiency (power conversionefficiency—PCE) (η) of the obtained device was carried out in acontrolled atmosphere (nitrogen) in a glove box at room temperature (25°C.). The current-voltage curves (I-V) were acquired with a Keithley®2600A multimeter connected to a personal computer for data collection.The photocurrent was measured by exposing the device to the light of anABET SUN® 2000-4 solar simulator, capable of providing 1.5G AM radiationwith an intensity of 100 mW/cm² (1 sun), measured with a powermeterOphir Nova® II connected to a 3A-P thermal sensor. The measurement wascarried out on 35 devices and the average value of photoelectricconversion efficiency (power conversion efficiency—PCE) (η) was equal to7.32%.

In order to establish the level of adhesion, on the semi-finished deviceafter the deposition of the double interlayer, i.e. after the depositionof the second anodic interlayer (buffer layer) and the first anodicinterlayer (buffer layer), a rectangle of adhesive tape was applied. Thetape was pressed with a finger and then torn off. The tear did not allowthe removal of any layers.

Example 2 (Comparative)

Solar Cell with Copolymer (Xb): PC₇₁BM and PEDOT:PSS

A polymer-based device was prepared on a substrate of polyethyleneterephthalate (PET) coated with ITO (indium tin oxide) (FomTechnologies—Denmark) (100 nm), previously subjected to a cleaningprocedure as described in the Example 1.

The deposition of the cathodic interlayer (buffer layer), the depositionof the active layer and the deposition of the first anodic interlayer(buffer layer), were carried out as described in Example 1; thecomposition of said cathodic interlayer (buffer layer), the compositionof said active layer and the composition of said first anodic interlayer(buffer layer), are the same as reported in Example 1; the thickness ofsaid cathodic interlayer (buffer layer), the thickness of said activelayer and the thickness of said first anodic interlayer (buffer layer),are the same as reported in Example 1.

Above the obtained active layer, unlike Example 1, the second anodicinterlayer (buffer layer) starting from a solution of phosphomolybdicacid trihydrate in iso-propanol was not deposited.

The deposition of the silver anode (Ag) was carried out as described inExample 1: the thickness of said silver anode is the same as reported inExample 1.

The thicknesses were measured with a Dektak 150 profilometer (VeecoInstruments Inc.).

The electrical characterization of the device, the current-voltagecurves (I-V) and the photocurrent, were measured as described inExample 1. The measurement was carried out on 35 devices and the averagevalue of photoelectric conversion efficiency (power conversionefficiency—PCE) (l) was equal to 6.06%.

In order to establish the level of adhesion, on the semi-finished deviceafter the deposition of the first anodic interlayer (buffer layer), arectangle of adhesive tape was applied. The tape was pressed with afinger and then tom off. The tear allowed the removal of the firstanodic interlayer (buffer layer).

Example 3 (Comparative)

Solar Cell with Copolymer (Xb):PC₇₁BM and Evaporated Molybdenum OxideMoO)

A polymer-based device was prepared on a substrate of polyethyleneterephthalate (PET) coated with ITO (indium tin oxide) (FomTechnologies—Denmark) (100 nm), previously subjected to a cleaningprocedure as described in the Example 1.

The deposition of the cathodic interlayer (buffer layer) and thedeposition of the active layer, were carried out as described in Example1; the composition of said cathodic interlayer (buffer layer) and thecomposition of said active layer are the same as reported in Example 1;the thickness of said cathodic interlayer (buffer layer) and thethickness of said active layer are the same as reported in Example 1.

Above the obtained active layer, unlike Example 1, neither the firstanodic interlayer (buffer layer) starting from a suspension comprisingPEDOT:PSS [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate](Clevios™ HTL Solar 388—Heraeus Co.), nor the second anodic interlayer(buffer layer) starting from a solution of phosphomolybdic acidtrihydrate in iso-propanol, were deposited.

Above the active layer instead, the anodic interlayer (buffer layer) wasdeposited, which was obtained by depositing molybdenum oxide (MoO₃)(Aldrich) through a thermal process: the thickness of the anodicinterlayer (buffer layer) was equal at 10 nm. The silver (Ag) anode,having a thickness of 100 nm, was deposited on the anodic interlayer(buffer layer) by vacuum evaporation, suitably masking the area of thedevice in order to obtain an active area equal to 0.25 mm².

The anodic interlayer (buffer layer) and the anode depositions werecarried out in a standard vacuum evaporation chamber containing thesubstrate and two evaporation vessels equipped with a heating resistancecontaining 10 mg of molybdenum oxide (MoO₃) powder (Aldrich) and 10shots of silver (Ag) (diameter 1 mm-3 mm) (Aldrich), respectively. Theevaporation process was carried out under vacuum, at a pressure of about1×10⁻⁶ bar. Molybdenum oxide (MoO₃) and silver (Ag), after evaporation,are condensed in the non-masked parts of the device.

The thicknesses were measured with a Dektak 150 profilometer (VeecoInstruments Inc.).

The electrical characterization of the device, the current-voltagecurves (I-V) and the photocurrent, were measured as described inExample 1. The measurement was carried out on 35 devices and the averagevalue of photoelectric conversion efficiency (power conversionefficiency—PCE) (η) was 6.74%.

In order toto establish the level of adhesion, on the semi-finisheddevice after the deposition of the anodic interlayer (buffer layer), arectangle of adhesive tape was applied. The tape was pressed with afinger and then torn off. The tear allowed the removal of the anodicinterlayer (buffer layer).

Example 4 (Disclosure)

Solar Cell with Copolymer (Xb):PC₇₁BM, PhosphomolybdicAcid/n-Dodecylamine and PEDOT:PSS

A polymer-based device was prepared on a substrate of polyethyleneterephthalate (PET) coated with ITO (indium tin oxide) (FomTechnologies—Denmark) (100 nm), previously subjected to a cleaningprocedure as described in the Example 1.

The deposition of the cathodic interlayer (buffer layer), the depositionof the active layer and the deposition of the first anodic interlayer(buffer layer), were carried out as described in Example 1; thecomposition of said cathodic interlayer (buffer layer) and thecomposition of said active layer are the same as reported in Example 1;the thickness of said cathodic interlayer (buffer layer) and thethickness of said active layer are the same as reported in Example 1.

Above the obtained active layer, unlike Example 1, the second anodicinterlayer (buffer layer) was deposited starting from a solution of 5.4mg/ml of phosphomolybdic acid trihydrate and 0.6 mg/ml of n-dodecylamine(Aldrich) in n-propanol: the deposit was carried out as described inExample 1.

The deposition of the silver (Ag) anode was carried out as described inExample 1: the thickness of said silver anode is the same as reported inExample 1.

The thicknesses were measured with a Dektak 150 profilometer (VeecoInstruments Inc.).

The electrical characterization of the device, the current-voltagecurves (I-V) and the photocurrent, were measured as described inExample 1. The measurement was carried out on 35 devices and the averagevalue of photoelectric conversion efficiency (power conversionefficiency—PCE)(q) was equal to 5.91%.

In order to establish the level of adhesion, on the semi-finished deviceafter the deposition of the double interlayer, i.e. after the depositionof the second anodic interlayer (buffer layer) and the first anodicinterlayer (buffer layer), a rectangle of adhesive tape was applied. Thetape was pressed with a finger and then torn off. The tear did not allowthe removal of any layers.

Example 5 (Disclosure)

Solar Cell with Copolymer (Xb):PC₇₁BM, Phosphomolybdic Acid/PFN andPEDOT:PSS

A polymer-based device was prepared on a substrate of polyethyleneterephthalate (PET) coated with ITO (indium tin oxide) (FomTechnologies—Denmark) (100 nm), previously subjected to a cleaningprocedure as described in the Example 1.

The deposition of the cathodic interlayer (buffer layer), the depositionof the active layer and the deposition of the first anodic interlayer(buffer layer), were carried out as described in Example 1; thecomposition of said cathodic interlayer (buffer layer) and thecomposition of said active layer are the same as reported in Example 1;the thickness of said cathodic interlayer (buffer layer) and thethickness of said active layer are the same as reported in Example 1.

On top of the obtained active layer, unlike Example 1, the second anodicinterlayer (buffer layer) was deposited starting from a solution of 5.5mg/ml of phosphomolybdic acid trihydrate and 0.5 mg/ml of poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)](PFN) (Aldrich) in tetrahydrofuran (Aldrich): the deposit was carriedout as described in Example 1.

The deposition of the silver anode (Ag) was carried out as described inExample 1: the thickness of said silver anode is the same as reported inExample 1.

The thicknesses were measured with a Dektak 150 profilometer (VeecoInstruments Inc.).

The electrical characterization of the device, the current-voltagecurves (I-V) and the photocurrent, were measured as described inExample 1. The measurement was carried out on 35 devices and the averagevalue of photoelectric conversion efficiency (power conversionefficiency—PCE) (l) was equal to 5.77%.

In order to establish the level of adhesion, on the semi-finished deviceafter the deposition of the double interlayer, i.e. after the depositionof the second anodic interlayer (buffer layer) and the first anodicinterlayer (buffer layer), a rectangle of adhesive tape was applied. Thetape was pressed with a finger and then torn off. The tear did not allowthe removal of any layers.

1. An inverted polymer photovoltaic cell (or solar cell) comprising: ananode; a first anodic interlayer (buffer layer) based on PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; an activelayer comprising at least one photoactive organic polymer as an electrondonor and at least one electron acceptor organic compound; a cathodicinterlayer (buffer layer); and a cathode; wherein a second anodicinterlayer (buffer layer) comprising at least one heteropolyacid and,optionally, at least one amino compound is placed between said firstanodic interlayer (buffer layer) and said active layer.
 2. The invertedpolymer photovoltaic cell (or solar cell) according to claim 1, whereinsaid anode is made of metal, said metal being selected from silver (Ag),gold (Au), aluminum (Al); or it consists of grids in conductivematerial, said conductive material being selected from silver (Ag),copper (Cu), graphite, graphene, and of a transparent conductivepolymer, said transparent conductive polymer being PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; or it consistsof an ink based on metal nanowires, said metal being selected fromsilver (Ag) and copper (Cu).
 3. The inverted polymer photovoltaic cell(or solar cell) according to claim 1, wherein said photoactive organicpolymer is selected from: (a) polythiophenes such as, for example,regioregular poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene),poly(3,4-ethylenedioxythiophene), or mixtures thereof, (b) alternatingor statistical conjugated copolymers comprising: at least onebenzotriazole (B) unit having general formula (Ia) or (Ib):

wherein group R is selected from alkyl groups, aryl groups, acyl groups,thioacyl groups, said alkyl, aryl, acyl and thioacyl groups beingoptionally substituted; at least one conjugated structural unit (A),wherein each unit (B) is connected to at least one unit (A) in any oneof the positions 4, 5, 6, or 7; (c) alternating conjugated copolymerscomprising benzothiadiazole units such as, for example, PCDTBT{poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]},PCPDTBT {poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]}; (d)alternating conjugated copolymers comprising thieno[3,4-b]pyrazidineunits; (e) alternating conjugated copolymers comprising quinoxalineunits; (f) alternating conjugated copolymers comprising monomer silolunits such as, for example, copolymers of 9,9-dialkyl-9-silafluorene;(g) alternating conjugated copolymers comprising condensed thiopheneunits such as, for example, copolymers of thieno[3,4-b]thiophene and ofbenzo[1,2-b: 4,5-b′]dithiophene; (h) alternating conjugated copolymerscomprising benzothiadiazole or naphthothiadiazole units substituted withat least one fluorine atom and thiophene units substituted with at leastone fluorine atom such as, for example, PffBT4T-2OD{poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)]},PBTff4T-2OD{poly[(2,1,3-benzothiadiazole-4,7-diyl)-alt-4′,3″-difluoro-3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophene-5,5′″-diyl)]},PNT4T-2OD{poly(naphtho[1,2-c:5,-c′]bis[1,2,5]thiadiazole-5,10-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophene-5,5′″-diyl)]}; (i) conjugated copolymerscomprising thieno[3,4-c]pyrrole-4,6-dione units such as PBDTTPD{poly[[5-(2-ethylhexyl)-[(5,6-dihydro-4,6-dioxo-4H-thieno[3,4-c]pyrrole-1,3-diyl)[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]};(l) conjugated copolymers comprising thienothiophene units such as PTB7{poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]},PBDB-T polymer{poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]};(m) polymers comprising a derivative of indacen-4-one having generalformula (III), (IV) or (V):

wherein: W and W₁, identical to or different from each other, representan oxygen atom; a sulfur atom; an N—R₃ group wherein R₃ represents ahydrogen atom, or is selected from C₁-C₂₀, linear or branched alkylgroups; Z and Y, identical to or different from each other, represent anitrogen atom; or a CR₄ group wherein R₄ represents a hydrogen atom, oris selected from C₁-C₂₀, linear or branched alkyl groups, optionallysubstituted cycloalkyl groups, optionally substituted aryl groups,optionally substituted heteroaryl groups, C₁-C₂₀, linear or branchedalkoxy groups, polyethyleneoxylic groups R₅—O—[CH₂—CH₂—O]_(n)— whereinR₅ is selected from C₁-C₂₀, linear or branched alkyl groups, and n is aninteger between 1 and 4, —R₆—OR₇ groups wherein R₆ is selected fromC₁-C₂₀, linear or branched alkylene groups and R₇ represents a hydrogenatom or is selected from C₁-C₂₀, linear or branched alkyl groups, or isselected from polyethyleneoxylic groups R₅—[—OCH₂—CH₂—]_(n)— wherein R₅has the same meanings reported above and n is an integer between 1 and4, —COR₈ groups wherein R₈ is selected from C₁-C₂₀, linear or branchedalkyl groups, —COOR₉ groups wherein R₉ is selected from C₁-C₂₀, linearor branched alkyl groups; or represent a —CHO group, or a cyano group(—CN); R₁ and R₂, identical to or different from each other, areselected from C₁-C₂₀, linear or branched alkyl groups; optionallysubstituted cycloalkyl groups; optionally substituted aryl groups;optionally substituted heteroaryl groups; C₁-C₂₀, linear or branchedalkoxy groups; polyethyleneoxylic groups R₅—O—[CH₂—CH₂—O]_(n)— whereinR₅ has the same meanings reported above and n is an integer between 1and 4; groups —R₆—OR₇ wherein R₆ and R₇ have the same meanings reportedabove; —COR₈ groups wherein R₈ has the same meanings reported above;—COOR₉ groups wherein R₉ has the same meanings reported above; orrepresent a —CHO group, or a cyano group (—CN); D represents an electrondonor group; A represents an electron acceptor group; n is an integerbetween 10 and 500; and (n) polymers comprising antradithiophenederivatives having general formula (X):

wherein: Z, identical to or different from each other, represent asulfur atom, an oxygen atom, a selenium atom; Y, identical to ordifferent from each other, represent a sulfur atom, an oxygen atom, aselenium atom; R₁, identical or different from each other, are selectedfrom amino groups —N—R₃R₄ wherein R₃ represents a hydrogen atom, or isselected from C₁-C₂₀, linear or branched alkyl groups, or is selectedfrom optionally substituted cycloalkyl groups and R₄ is selected fromC₁-C₂₀, linear or branched alkyl groups, or is selected from optionallysubstituted cycloalkyl groups; or are selected from C₁-C₃₀, linear orbranched alkoxy groups; or are selected from polyethyleneoxylic groupsR₅—O—[CH₂—CH₂—O]_(n)— wherein R₅ is selected from C₁-C₂₀, linear orbranched alkyl groups, and n is an integer between 1 and 4; or areselected from —R₆—OR₇ groups wherein R₆ is selected from C₁-C₂₀, linearor branched alkylene groups and R₇ represents a hydrogen atom, or isselected from C₁-C₂₀, linear or branched alkyl groups, or is selectedfrom polyethyleneoxyl groups R₅—[—OCH₂—CH₂—]_(n)— wherein R₅ has thesame meanings reported above and n is an integer between 1 and 4; or areselected from thiol groups —S—R₈ wherein R₈ is selected from C₁-C₂₀,linear or branched alkyl groups; R₂, identical to or different from eachother, represent a hydrogen atom; or are selected from C₁-C₂₀, linear orbranched alkyl groups; or are selected from —COR₉ groups wherein R₉ isselected from C₁-C₂₀, linear or branched alkyl groups; or are selectedfrom —COOR₁₀ groups wherein R₁₀ is selected from C₁-C₂₀, linear orbranched alkyl groups; or are selected from optionally substituted arylgroups; or are selected from optionally substituted heteroaryl groups; Arepresents an electron acceptor group; n is an integer between 10 and500; selected from: PffBT4T-2OD{poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)]},PBDTTPD{poly[[5-(2-ethylhexyl)-5,6-dihydro-4,6-dioxo-4H-thieno[3,4-c]pyrrole-1,3-diyl)[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]},PTB7{poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]},PBDB-T{poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]};polymers comprising antradithiophene derivatives having general formula(X).
 4. The inverted polymer photovoltaic cell (or solar cell) accordingto claim 1, wherein said organic electron acceptor compound is selectedfrom: fullerene derivatives such as [6,6]-phenyl-C₆₁-butyric acid methylester (PCBM), [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM),indene-C₆₀ bis-adduct (ICBA),bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C₆₂ (Bis-PCBM);selected from [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM),[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM); or non-fullerenecompounds, optionally polymeric, such as compounds based onperylene-diimides or naphthalene-diimides and fused aromatic rings;indacenothiophenes with electron-poor terminal groups; compounds havingan aromatic core capable of symmetrical rotation, such as derivatives ofcorannulene or truxenone; from:3,9-bis{2-methylene-[3-(1,1-dicyanomethylene)-indanone]}-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3‘-d’]-s-indacene[1,2-b:5,6-b′]-dithiophene,poly{[N,N-bis(2-octyldodecyl)-1,4,5,8-naphthalenediamine-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}.5. The inverted polymer photovoltaic cell (or solar cell) according toclaim 1, wherein said cathodic interlayer (buffer layer) comprises zincoxide, titanium oxide.
 6. The inverted polymer photovoltaic cell (orsolar cell) according to claim 1, wherein said cathode is of a materialselected from: indium-tin oxide (ITO), fluorine-doped tin oxide (FTO),zinc oxide doped with aluminium (AZO), zinc oxide doped with gadoliniumoxide (GZO); or it consists of grids in conductive material, saidconductive material being selected from silver (Ag), copper (Cu),graphite, graphene, and of a transparent conductive polymer, saidtransparent conductive polymer being PEDOT:PSS[poly(3,4-ethylenedioxythiophene):polystyrene sulfonate]; or it consistsof an ink based on metal nanowires, said metal being selected fromsilver (Ag), copper (Cu).
 7. The inverted polymer photovoltaic cell (orsolar cell) according to claim 1, wherein said cathode is associatedwith a support layer which is of transparent rigid material such asglass, or of flexible material such as polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyethyleneimine (PI), polycarbonate(PC), polypropylene (PP), polyimide (PI), triacetyl cellulose (TAC), orcopolymers thereof.
 8. The inverted polymer photovoltaic cell (or solarcell) according to claim 1, wherein said at least one heteropolyacid isselected from heteropolyacids having general formula (I):H_(x)[A(MO₃)_(y)O_(z)]  (I) wherein: A represents a silicon atom, or aphosphorus atom; M represents an atom of a transition metal belonging togroup 5 or 6 of the Periodic Table of the Elements, x is an integer thatdepends on the valence of A; y is 12 or 18; z is 4 or
 6. 9. The invertedpolymer photovoltaic cell (or solar cell) according to claim 1, whereinsaid at least one heteropolyacid is selected from heteropolyacids havinggeneral formula (II):H_(x)[A(MO)_(p)(V)_(q)O₄₀]  (II) wherein: A represents a silicon atom,or a phosphorus atom; x is an integer that depends on the valence of A;p is 6 or 10; q is 2 or
 6. 10. The inverted polymer photovoltaic cell(or solar cell) according to claim 8, wherein said at least oneheteropolyacid is selected from: hydrated phosphomolybdic acid{H₃[P(MoO₃)₁₂O₄]·nH₂O}, phosphomolybdic acid {H₃[P(MoO₃)₁₂O₄]} inalcoholic solution, hydrated phosphotungstic acid {H₃[P(WO₃)₁₂O₄]·nH₂O},phosphotungstic acid in alcoholic solution {H₃[P(WO₃)₁₂O₄]}, hydratedsilicomolybdic acid {H₄[Si(MoO₃)₁₂O₄]·nH₂O}, silicomolybdic acid{H₄[Si(MoO₃)₁₂O₄]} in alcoholic solution, hydrated silicotungstic acid{H₄[Si(WO₃)₁₂O₄]·nH₂O}, silicotungstic acid {H₄[Si(WO₃)₁₂O₄]} inalcoholic solution, hydrated phosphomolybdovanadic acid{H₃[P(Mo)₆(V)₆O₄₀]·nH₂O}, phosphomolybdovanadic acid {H₃[P(Mo)₆(V)₆O₄₀]}in alcoholic solution, hydrated phosphomolybdovanadic acid{H₃[P(Mo)₁₀(V)₂O₄₀]·nH₂O}, phosphomolybdovanadic acid{H₃[P(Mo)₁₀(V)₂O₄₀]} in alcoholic solution or mixtures thereof.
 11. Theinverted polymer photovoltaic cell (or solar cell) according to claim 1,wherein said amino compound is selected from: low molecular weightaliphatic amines, containing from 8 to 24 carbon atoms, linear orbranched, primary, secondary or tertiary, such as n-octylamine,n-dodecylamine, n-hexadecylamine, di-n-octylamine, or mixtures thereof;conjugated polymers containing chain or side amino groups such aspoly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA),poly(N,N-bis-4-butylphenyl-N,N-bisphenyl)benzidine (polyTPD),poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)](PFN), or mixtures thereof; or mixtures thereof.
 12. A process forpreparing the inverted polymer photovoltaic cell (or solar cell)according to claim 1, the process including the following steps: formingthe cathode by sputtering; or by electron beam assisted deposition; orby depositing a transparent conductive polymer via spin coating, orgravure printing, or flexographic printing, or slot die coating,preceded by deposition of grids in conductive material via evaporation,or screen-printing, or spray-coating, or flexographic printing; or bydepositing an ink based on metal nanowires via spin coating, or gravureprinting, or flexographic printing, or slot die coating; forming thecathodic interlayer (buffer layer) by spin coating, or gravure printing,or flexographic printing, or slot die coating above said cathode;forming the active layer by spin coating, or gravure printing, orslot-die coating, above said cathodic interlayer (buffer layer); formingthe second anodic interlayer (buffer layer) by spin coating, or gravureprinting, or screen-printing, or flexographic printing, or slot-diecoating above said active layers; forming the first anodic interlayer(buffer layer) by spin coating, or gravure printing, or screen-printing,or flexographic printing, or slot-die coating, above said second anodicinterlayer (buffer layer); and forming the anode by vacuum evaporation,or screen-printing, or spray-coating, or flexographic printing, abovesaid first anodic interlayer (buffer layer); or by deposition of atransparent conductive polymer via spin coating, or gravure printing, orflexographic printing, or slot die coating, followed by deposition ofgrids in conductive material via evaporation, or screen-printing, orspray-coating, or flexographic printing, above said first anodicinterlayer (buffer layer); or by deposition of an ink based on metalnanowires via spin coating, or gravure printing, or flexographicprinting, or slot die coating, above said first anodic interlayer(buffer layer).
 13. The inverted polymer photovoltaic cell (or solarcell) according to claim 1, wherein: the anode has a thickness rangingbetween 50 nm and 150 nm; the first anodic interlayer (buffer layer) hasa thickness ranging between 10 nm and 2000 nm; the second anodicinterlayer (buffer layer) has a thickness ranging between 1 nm and 100nm; the active layer has a thickness ranging between 50 nm and 500 nm;the cathodic interlayer (buffer layer) has a thickness ranging between10 nm and 100 nm; and the cathode has a thickness ranging between 50 nmand 150 nm.